1. Field of the Invention
This invention relates to a micro structured electrode and method for monitoring wafer electroplating baths that permits in situ monitoring of the electrodeposition process during the manufacture of micro structured electrodes, typically for use in the semiconductor industry.
2. Description of Prior Art
The semiconductor industry is replacing aluminum and tungsten with copper as the conductive material for chip interconnects and vias. The current technology for depositing copper onto the wafer is by an advanced electroplating method that utilizes specially designed plating cells and plating baths that enable copper deposition into the small geometries used in chip manufacturing. The baths consist of a solution of copper sulfate, sulfuric acid, chloride, and other additives, called levelers, brighteners, and accelerators, that enhance the deposition process. Maintaining the additives in a specific range is critical to defect-free copper deposition.
For example, Robertson, et al., Galvanostatic Method for Quantification of Organic Suppressor and Accelerator Additives in Acid Copper Plating Baths, suggests that the concentration of the organic additives in the plating bath is important to the success of void-free metal deposition. Describing a proposed method of bath condition analysis, a pulsed cyclic galvanostatic analysis (PCGA) is based on the measurement of the plating overvoltage as a function of the additive concentration, and relies on the use of a nucleate pulse.
Kelly, et al., Leveling and Microstructural Effects of Additives for Copper Electrodeposition, 146 J. Electrochemical Soc., 2540–2549 (1999), discloses the role of two model additives in the deposition of copper from an acid-copper sulfate electrolyte.
In Bratin, et al., Control of Damascene Copper Processes by Cyclic Voltammetric Stripping, Semiconductor Fabtech, 12th Edition, the shift from aluminum to copper as the metal of choice in chip interconnects for the semiconductor industry is disclosed. The reference further suggests that organic additives are useful to control the uniformity of copper deposition, and that very close control of the additive levels in the copper bath is required.
Lindner, Microfabricated Potentiometric Electrodes and Their in Vivo Applications, Analytical Chemistry, May 1, 2000, discloses microelectrodes used in biology and medicine. These microelectrodes are not microstructured, but are rather flat, micro-sized devices.
Dionex, Analysis of Copper Plating Baths, an industry brief indicating that it was presented at the 1998 Semicon Southwest Int'l Electronics Mfg. Symposium, suggests the shift from aluminum to copper as the metal of choice in chip interconnects for the semiconductor industry. The article further suggests that, for microelectronics, an acid copper sulfate plating solution is optimal due to its high throwing power. This article then goes on to describe a copper bath analysis method using ion and high performance liquid chromatography.
In sales literature, Technic, Inc. describes its RTA as an automated, online, real-time, in situ system for monitoring and controlling the chemical composition of baths at its website, http://www.technic.com/resrch/rta.htm. This equipment purports to offer a single instrument that can be operated remotely without extensive operator training. U.S. patents of interest in this regard include U.S. Pat. Nos. 5,391,271, 5,336,380, 5,324,400, 5,320,724, 5,298,131, 5,298,130, 5,298,129, 5,296,124, 5,296,123, and 4,631,116.
Thus, frequent measurement of the additive concentrations is needed to maintain the proper bath concentrations of the additives. Currently, this is done by electrochemical techniques, such as (1) cyclic voltammetric stripping (CVS), presently utilized by ECI Technology in laboratory and online equipment; (2) pulsed cyclic galvanostatic analysis (PCGS), presently sold by ATMI; and (3) alternating current voltammetry (AC voltammetry), presently sold by Technic, Inc. in its RTA™ analyzer.
These methods were developed for printed circuit board plating applications as offline analytical measurements, but recently have been incorporated into online monitoring equipment and connected to the copper interconnect plating bath distribution system. They utilize planar, metal electrodes and potential versus current scans to calculate additive concentrations. Presently, a disadvantage of these techniques is that they take too much time to obtain a measurement, sometimes up to two hours for one additive concentration. This is due to the additional preparation and calibration required with the multi-component plating bath solution. Another problem associated with these methods is that the reliability and accuracy of the measurements are insufficient for the integrated circuit manufacturing industry. Often, the measurement signal drifts and frequent maintenance of the electrodes is needed. In addition, it is not clear how the bulk additive concentration levels or degradation products from the plating process correlate with the deposition rate of the copper and the onset of defects and voids in the interconnects and vias. It is believed that the mass transfer characteristics of the additives plays a crucial role in the copper deposition and may be a more important measure of the condition of the bath.
Thus, a problem associated with methods for monitoring wafer electroplating baths that permits in situ monitoring of the electrodeposition process during the manufacture of metallic interconnects is that they require too much time to prepare and operate, and thus cannot communicate environment conditions quickly enough to be optimally useful.
Yet another problem associated with methods for monitoring wafer electroplating baths that permits in situ monitoring of the electrodeposition process during the manufacture of metallic interconnects is that they are not easily prepared, and therefore require greater skill and knowledge during the preparation of the monitoring process.
Still a further problem associated with methods for monitoring wafer electroplating baths that permits in situ monitoring of the electrodeposition process during the manufacture of metallic interconnects is that they require a difficult calibration, and are therefore susceptible to human error and/or machine error.
An even further problem associated with methods for monitoring wafer electroplating baths that permits in situ monitoring of the electrodeposition process during the manufacture of metallic interconnects is that they are not sufficiently reliable, and can lead to process errors that are detrimental to the manufacturing process.
Another problem associated with methods for monitoring wafer electroplating baths that permits in situ monitoring of the electrodeposition process during the manufacture of metallic interconnects is that they are not sufficiently accurate to provide data that effectively minimizes the production variances to an acceptable level in the semiconductor field.
For the foregoing reasons, there has been defined a long felt and unsolved need for a method for monitoring wafer electroplating baths that permits in situ monitoring of the electrodeposition process during the manufacture of metallic interconnects that seeks to overcome the problems discussed above, while at the same time providing a simple, easily used method for monitoring wafer electroplating baths and a microstructured electrode manufactured thereby.